Coating apparatus and method

ABSTRACT

The invention is an alternative to a conventional atomizing coating apparatus. The apparatus and associated coating methodology of the invention provides a uniform atomized fluid stream, and, in turn, a uniform coating to an object on an industrial scale. The apparatus and methodology addresses many of the critical parameters associated with the conventional curtain and atomizing coating techniques, including but no limited to, uniform distribution, acoustical transparency, reduction or elimination of clogged nozzles, and elimination of the need for reciprocating nozzles.

FIELD OF THE INVENTION

The invention relates to a coating apparatus, and, more specifically, toan improved coating apparatus which provides a longitudinally extending,uniform, atomized coating stream.

BACKGROUND OF THE INVENTION

A critical issue for manufacturers of coating equipment is the need tomeet customer demands for increased efficiencies in the coatingapplication process. Regardless of the coating type or applicationmethodology, uniformity of application and transfer efficiency arecritical parameters that continue to be addressed by research anddevelopment efforts.

Selection of the appropriate application methodology depends not only onthe type of coating but also on the requirements of the substrate towhich it is applied.

For example, where the acoustical capabilities of an object are soughtto be maintained, it is widely known in the coatings art that it iscritical for the coating to have little or no impact on acousticalperformance of the material, i.e. the coating is acousticallytransparent. It is also widely known that the acoustical performance ofa material is impacted by both the uniformity of application as well asthe thickness of the coating. Thus, obtaining the optimal performance ofa material, such as an acoustical fibrous mat, requires a minimumdeviation of acoustic capability across the entire surface of thematerial.

One well known large-scale, i.e. industrial-scale, atomization techniquewhich provides acoustical transparency and wide-area coverage isillustrated in prior art FIG. 1. This conventional large-scale coatingtechnique utilizes a series of single-point atomizing spray guns, ornozzles. This system is commonly known in the industry as an overlap, ormulti-tip header. As shown in FIG. 1, each nozzle 1A-1E, commonlyreferred to in the art as a single-point nozzle, produces an atomizedfluid stream, 3A-3E respectively, which spreads out, or diverges, into aconical spray pattern. To ensure complete coverage across a large width,the outer portions of the atomized fluid streams 3A-3A must overlap.Though undetectable to the naked eye, these overlapping streams do notuniformly apply the coating.

To approach uniformity of application using overlap header technology,several features can be manipulated, including: the spacing of thenozzles; the spacing between the overlap header and the object to becoated; the tip geometry of the nozzles; and the flow rate of the fluidpassing through the nozzles. However, it is widely known and understoodby those of ordinary skill in the art that overlap header technologyassumes a density gradient for each nozzle, and, thus, the effort toapproach uniformity of application is an iterative process that isfundamentally variable.

One skilled in the art further understands that it is impossible tocompletely eliminate defects such as streaks and shade variation usingan overlap header. A conventional attempt to randomize these defects isto use cyclically traversing, i.e. reciprocating, multi-tip headersinstead of multi-tip fixed headers. Conventional wisdom is thatrandomizing these defects will in effect disguise the defects and makethem undetectable to the naked eye.

Unfortunately, both fixed and reciprocation headers add cost to thefinal product. For example, as the tip of each gun gradually wears oreven becomes clogged, the spray pattern of the gun will change andultimately lead to a more non-uniform application. Also, frequentinterruptions due to cleaning or replacement of the tips addsconsiderable expense in terms of the downtime required and the cost ofthe replacement part. Thus, an alternative large-scale technique whichaddresses the issues with existing techniques is needed.

SUMMARY

The present invention is an industrial-scale coating apparatus forapplying a liquid coating to the surface of a sound absorbing material.The apparatus includes a longitudinally extending discharge nozzlehaving a specified length. The nozzle discharges a linear stream ofatomized droplets at a uniform velocity along the entire specifiedlength of the nozzle.

The present invention further includes an improved methodology of spraycoating a moving object on an industrial scale. The method includes thesteps of: (a) providing an industrial-scale coating apparatus having alongitudinally extending discharge nozzle having a specified length; (b)positioning the coating apparatus above a conveyor, the conveyor havinga direction of travel such that the longitudinally extending dischargenozzle extends in a direction transverse the direction of travel of aconveyor; and (c) discharging a linear stream of atomized droplets ontothe surface of an object moving on the conveyor, the linear stream ofatomized droplets being discharged from the nozzle at a uniform velocityalong the entire specified length of the nozzle.

The improved coating apparatus and spray coating methodology areparticularly useful in applying a liquid coating to the surface of amaterial that requires a minimum deviation in acoustic capability acrossthe entire surface of the material for optimum performance. Theapparatus and methodology are also useful when a minimal deviation ofone or more of light reflectance, color, and gloss capability of thematerial is desired. Additional advantages include, but are not limitedto: the elimination of visual defects created by multiple atomizingstreams; the elimination of the use of a multiple atomizing streamsutilizing the technique of reciprocation to randomize visual defects;and the elimination of the cost of and the maintenance of multiple,single-point atomizing spray nozzles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view of a prior art coating apparatus utilizingmultiple single-point atomizing spray nozzles.

FIG. 2 is a perspective view of a portion of a coating system utilizingthe coating apparatus of the invention.

FIG. 3 is a perspective view in partial cross-section of an exampleembodiment of the coating apparatus of the invention.

FIG. 4 is a cross sectional view of the example embodiment illustratedin FIG. 3.

FIG. 5 is a perspective view in partial cross-section of a secondexample embodiment of the coating apparatus of the invention.

FIG. 6 is a cross sectional view of the example embodiment illustratedin FIG. 5.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is now made to the drawings wherein similar components bearthe same reference numerals throughout the several views.

The improved atomizing apparatus can be utilized in conventionalindustrial-scale coating systems, including systems having alongitudinally extending conveyor which transports the object ormaterial to be coated through a coating station such as illustrated inFIG. 1. As shown, the atomizing apparatus 10 is positioned above aconveyor 11, or backing roller, in spaced relation, thereby forming a“coating zone”. The conveyor 11 has a direction of travel indicated byArrow C. The apparatus 10 is positioned in a direction transverse to thedirection of travel of the conveyor 11. As shown, an uninterruptedstream of atomized coating material 20 is discharged onto the surface ofan object 22, such as an acoustical ceiling tile, at an application ratethat is uniform across the entire length of the discharge nozzle 16,and, in turn, the entire length of the object 22.

FIGS. 3 and 4 illustrate a first example embodiment of the improvedindustrial size coating apparatus 10 in greater detail. The coatingapparatus 10 includes a generally linear, longitudinally extendinghousing structure 12. The housing structure 12 includes a hopper 14,which houses liquid coating material. The liquid coating materialtypically used to coat materials on an industrial-sized scale, such asliquid coating material for acoustical ceiling tiles, includes about 40%to about 70% solids by weight, and preferably from about 50% to about60% solids by weight.

In the embodiments shown throughout the drawings, the hopper 14 extendslongitudinally and substantially the entire length of the housingstructure 12. As best seen in FIG. 4, at the base of the hopper 14 is alinear discharge nozzle 16 which, although not required, may also extendsubstantially the entire length of the housing structure 12. Typically,the liquid coating material is permitted to flow from the hopper 14 andthrough the linear discharge nozzle 16 by gravity.

The housing structure 12 further includes a first air stream 18 and asecond air stream 19. Both air streams 18, 19 extend in the longitudinaldirection and are positioned in parallel relation with the lineardischarge nozzle 16. The outlets of the air streams 18, 19 arepositioned proximate the linear discharge nozzle 16. High velocity airflows through the air streams as illustrated by arrow F, and ultimatelyimpinges on the liquid coating material as the fluid exits the lineardischarge nozzle 16. Preferably, the air stream outlets are positionedbehind, e.g. above, the outlet of the discharge nozzle so that the highvelocity air causes the liquid coating to rush toward the object to becoated as an uninterrupted, uniform, longitudinally extending stream ofatomized fluid droplets 20 having a longitudinally extending fan radius.By way of comparison, when a stream of air impinges on the coatingstream in a conventional atomization spray apparatus, such asatomization spray apparatus illustrated in FIG. 1, the atomized dropletsform a circular fan radius.

FIGS. 5 and 6 illustrate a second example embodiment of the coatingapparatus of the invention. The second example embodiment includes allof the features described above with respect to the first exampleembodiment. In addition, at the base of this coating apparatus 10′ is acap 25 which provides an area for internal mixing of the air and liquidcoating prior to exiting the apparatus 10. For purposes of thisdescription, internal air mixing is defined as a fluid stream beingmixed within the confines of the coating apparatus. The cap 25 includesfirst and second side walls, 27 and 28 respectively. At least a portionof each sidewall 27, 28 is disposed at an angle so as to form a linearopening 32 therebetween. The linear cap opening 32 is preferably inalignment with the linear discharge nozzle 16. Furthermore, the lengthof the linear cap opening 32 is preferably substantially the same lengthas the longitudinally extending linear nozzle 16 and air streams 18, 19.

The above description of the invention is provided as an enablingteaching of the invention in its best, currently known embodiment. Itwill be understood by those of skill in the art that variations on theembodiments set forth herein are possible and within the scope of thepresent invention. The embodiments set forth above and many otheradditions, deletions, and modifications may be made by those of skill inthe art without departing from the spirit and scope of the invention.

For example, the apparatus 10, 10′ may also utilize external airassistance. For purposes of this description, “external air assistance”means that the air is added by means of an air stream outside thecomponents of the coating apparatus such as air generated via linear airknives or jets which are known in the art. External air assistance willfurther atomize the stream of atomized fluid droplets and maintainuniformity. Depending on the angle on impingement, the external airassistance may increase the speed of the droplets 20 towards the spraytarget.

I claim:
 1. An industrial-scale atomizing apparatus for applying aliquid coating, the apparatus comprising: a hopper containing the liquidcoating; a discharge nozzle having an elongated slot outlet having alength that extends along a longitudinal axis, the discharge nozzlefluidly coupled to the hopper so that the liquid coating flows from thehopper and through the elongated slot outlet by gravity; a first airstream having an elongated slot outlet that extends substantiallyparallel to the elongated slot outlet of the discharge nozzle; a secondair stream having an elongated slot outlet that extends substantiallyparallel to the elongated slot outlet of the discharge nozzle, the firstand second air streams positioned proximate the discharge nozzle; theelongated slot outlets of the first and second air streams positionedabove the elongated slot outlet, wherein the elongated slot outlet ofthe discharge nozzle discharges a liquid stream of atomized droplets ofthe liquid coating at a substantially uniform velocity along the lengthof the elongated slot outlet of the discharge nozzle in a longitudinallyextending fan pattern; and wherein the first air stream is isolated fromthe liquid coating prior to exiting the elongated slot outlet of thefirst air stream, and the second air stream is isolated from the liquidcoating prior to exiting the elongated slot outlet of the second airstream; wherein each of the first and second air streams extendlongitudinally and in parallel relation to the discharge nozzle.
 2. Theindustrial-scale atomizing apparatus of claim 1, wherein the liquidcoating comprises from about 40% to about 70% solids by weight.
 3. Theindustrial-scale atomizing apparatus of claim 2, wherein the liquidcoating comprises from about 50% to about 60% solids by weight.
 4. Theindustrial-scale atomizing apparatus of claim 1, whereby a minimumdeviation is achieved in acoustic capability of an acoustical materialto which the liquid coating is applied.
 5. The industrial-scaleatomizing apparatus of claim 1, whereby the apparatus provides a coatingwhich has minimal impact on the light reflectance, color, and gloss ofthe material to which the coating is applied.